Structure of the WYL-domain containing transcription activator, DriD, in complex with ssDNA effector and DNA target site.

Transcription regulators play central roles in orchestrating responses to changing environmental conditions. Recently the Caulobacter crescentus transcription activator DriD, which belongs to the newly defined WYL-domain family, was shown to regulate DNA damage responses independent of the canonical SOS pathway. However, the molecular mechanisms by which DriD and other WYL-regulators sense environmental signals and recognize DNA are not well understood. We showed DriD DNA-binding is triggered by its interaction with ssDNA, which is produced during DNA damage. Here we describe the structure of the full-length C. crescentus DriD bound to both target DNA and effector ssDNA. DriD consists of an N-terminal winged-HTH (wHTH) domain, linker region, three-helix bundle, WYL-domain and C-terminal WCX-dimer domain. Strikingly, DriD binds DNA using a novel, asymmetric DNA-binding mechanism that results from different conformations adopted by the linker. Although the linker does not touch DNA, our data show that contacts it makes with the wHTH are key for specific DNA binding. The structure indicates how ssDNA-effector binding to the WYL-domain impacts wHTH DNA binding. In conclusion, we present the first structure of a WYL-activator bound to both effector and target DNA. The structure unveils a unique, asymmetric DNA binding mode that is likely conserved among WYL-activators.

M. mazei glutamine synthetase and glutamine synthetase-GlnK1 structures reveal enzyme regulation by oligomer modulation.

Glutamine synthetases (GS) play central roles in cellular nitrogen assimilation. Although GS active-site formation requires the oligomerization of just two GS subunits, all GS form large, multi-oligomeric machines. Here we describe a structural dissection of the archaeal Methanosarcina mazei (Mm) GS and its regulation. We show that Mm GS forms unstable dodecamers. Strikingly, we show this Mm GS oligomerization property is leveraged for a unique mode of regulation whereby labile Mm GS hexamers are stabilized by binding the nitrogen regulatory protein, GlnK1. Our GS-GlnK1 structure shows that GlnK1 functions as molecular glue to affix GS hexamers together, stabilizing formation of GS active-sites. These data, therefore, reveal the structural basis for a unique form of enzyme regulation by oligomer modulation.

Structures of the DarR transcription regulator reveal unique modes of second messenger and DNA binding.

The mycobacterial repressor, DarR, a TetR family regulator (TFR), was the first transcription regulator shown to bind c-di-AMP. However, the molecular basis for this interaction and the mechanism involved in DNA binding by DarR remain unknown. Here we describe DarR-c-di-AMP and DarR-DNA structures and complementary biochemical assays. The DarR-c-di-AMP structure reveals a unique effector binding site for a TFR, located between DarR dimer subunits. Strikingly, we show this motif also binds cAMP. The location of the adenine nucleotide binding site between subunits suggests this interaction may facilitate dimerization and hence DNA binding. Indeed, biochemical assays show cAMP enhances DarR DNA binding. Finally, DarR-DNA structures reveal a distinct TFR DNA-binding mechanism involving two interacting dimers on the DNA. Thus, the combined data unveil a newly described second messenger binding motif and DNA binding mode for this important family of regulators.

Structure of the T. brucei kinetoplastid RNA editing substrate-binding complex core component, RESC5.

Kinetoplastid protists such as Trypanosoma brucei undergo an unusual process of mitochondrial uridine (U) insertion and deletion editing termed kinetoplastid RNA editing (kRNA editing). This extensive form of editing, which is mediated by guide RNAs (gRNAs), can involve the insertion of hundreds of Us and deletion of tens of Us to form a functional mitochondrial mRNA transcript. kRNA editing is catalyzed by the 20 S editosome/RECC. However, gRNA directed, processive editing requires the RNA editing substrate binding complex (RESC), which is comprised of 6 core proteins, RESC1-RESC6. To date there are no structures of RESC proteins or complexes and because RESC proteins show no homology to proteins of known structure, their molecular architecture remains unknown. RESC5 is a key core component in forming the foundation of the RESC complex. To gain insight into the RESC5 protein we performed biochemical and structural studies. We show that RESC5 is monomeric and we report the T. brucei RESC5 crystal structure to 1.95 Å. RESC5 harbors a dimethylarginine dimethylaminohydrolase-like (DDAH) fold. DDAH enzymes hydrolyze methylated arginine residues produced during protein degradation. However, RESC5 is missing two key catalytic DDAH residues and does bind DDAH substrate or product. Implications of the fold for RESC5 function are discussed. This structure provides the first structural view of an RESC protein.

Allosteric regulation of glycogen breakdown by the second messenger cyclic di-GMP.

Streptomyces are our principal source of antibiotics, which they generate concomitant with a complex developmental transition from vegetative hyphae to spores. c-di-GMP acts as a linchpin in this transition by binding and regulating the key developmental regulators, BldD and WhiG. Here we show that c-di-GMP also binds the glycogen-debranching-enzyme, GlgX, uncovering a direct link between c-di-GMP and glycogen metabolism in bacteria. Further, we show c-di-GMP binding is required for GlgX activity. We describe structures of apo and c-di-GMP-bound GlgX and, strikingly, their comparison shows c-di-GMP induces long-range conformational changes, reorganizing the catalytic pocket to an active state. Glycogen is an important glucose storage compound that enables animals to cope with starvation and stress. Our in vivo studies reveal the important biological role of GlgX in Streptomyces glucose availability control. Overall, we identify a function of c-di-GMP in controlling energy storage metabolism in bacteria, which is widespread in Actinobacteria.

Molecular Analysis of pSK1 par: A Novel Plasmid Partitioning System Encoded by Staphylococcal Multiresistance Plasmids.

The segregation of prokaryotic plasmids typically requires a centromere-like site and two proteins, a centromere-binding protein (CBP) and an NTPase. By contrast, a single 245 residue Par protein mediates partition of the prototypical staphylococcal multiresistance plasmid pSK1 in the absence of an identifiable NTPase component. To gain insight into centromere binding by pSK1 Par and its segregation function we performed structural, biochemical and in vivo studies. Here we show that pSK1 Par binds a centromere consisting of seven repeat elements. We demonstrate this Par-centromere interaction also mediates Par autoregulation. To elucidate the Par centromere binding mechanism, we obtained a structure of the Par N-terminal DNA-binding domain bound to centromere DNA to 2.25 Å. The pSK1 Par structure, which harbors a winged-helix-turn-helix (wHTH), is distinct from other plasmid CBP structures but shows homology to the B. subtilis chromosome segregation protein, RacA. Biochemical studies suggest the region C-terminal to the Par wHTH forms coiled coils and mediates oligomerization. Fluorescence microscopy analyses show that pSK1 Par enhances the separation of plasmids from clusters, driving effective segregation upon cell division. Combined the data provide insight into the molecular properties of a single protein partition system.

Molecular dissection of the glutamine synthetase-GlnR nitrogen regulatory circuitry in Gram-positive bacteria.

How bacteria sense and respond to nitrogen levels are central questions in microbial physiology. In Gram-positive bacteria, nitrogen homeostasis is controlled by an operon encoding glutamine synthetase (GS), a dodecameric machine that assimilates ammonium into glutamine, and the GlnR repressor. GlnR detects nitrogen excess indirectly by binding glutamine-feedback-inhibited-GS (FBI-GS), which activates its transcription-repression function. The molecular mechanisms behind this regulatory circuitry, however, are unknown. Here we describe biochemical and structural analyses of GS and FBI-GS-GlnR complexes from pathogenic and non-pathogenic Gram-positive bacteria. The structures show FBI-GS binds the GlnR C-terminal domain within its active-site cavity, juxtaposing two GlnR monomers to form a DNA-binding-competent GlnR dimer. The FBI-GS-GlnR interaction stabilizes the inactive GS conformation. Strikingly, this interaction also favors a remarkable dodecamer to tetradecamer transition in some GS, breaking the paradigm that all bacterial GS are dodecamers. These data thus unveil unique structural mechanisms of transcription and enzymatic regulation.

ssDNA is an allosteric regulator of the C. crescentus SOS-independent DNA damage response transcription activator, DriD.

DNA damage repair systems are critical for genomic integrity. However, they must be coordinated with DNA replication and cell division to ensure accurate genomic transmission. In most bacteria, this coordination is mediated by the SOS response through LexA, which triggers a halt in cell division until repair is completed. Recently, an SOS-independent damage response system was revealed in Caulobacter crescentus. This pathway is controlled by the transcription activator, DriD, but how DriD senses and signals DNA damage is unknown. To address this question, we performed biochemical, cellular, and structural studies. We show that DriD binds a specific promoter DNA site via its N-terminal HTH domain to activate transcription of genes, including the cell division inhibitor didA A structure of the C-terminal portion of DriD revealed a WYL motif domain linked to a WCX dimerization domain. Strikingly, we found that DriD binds ssDNA between the WYL and WCX domains. Comparison of apo and ssDNA-bound DriD structures reveals that ssDNA binding orders and orients the DriD domains, indicating a mechanism for ssDNA-mediated operator DNA binding activation. Biochemical and in vivo studies support the structural model. Our data thus reveal the molecular mechanism underpinning an SOS-independent DNA damage repair pathway.

DNA mismatches reveal conformational penalties in protein-DNA recognition.

Transcription factors recognize specific genomic sequences to regulate complex gene-expression programs. Although it is well-established that transcription factors bind to specific DNA sequences using a combination of base readout and shape recognition, some fundamental aspects of protein-DNA binding remain poorly understood1,2. Many DNA-binding proteins induce changes in the structure of the DNA outside the intrinsic B-DNA envelope. However, how the energetic cost that is associated with distorting the DNA contributes to recognition has proven difficult to study, because the distorted DNA exists in low abundance in the unbound ensemble3-9. Here we use a high-throughput assay that we term SaMBA (saturation mismatch-binding assay) to investigate the role of DNA conformational penalties in transcription factor-DNA recognition. In SaMBA, mismatched base pairs are introduced to pre-induce structural distortions in the DNA that are much larger than those induced by changes in the Watson-Crick sequence. Notably, approximately 10% of mismatches increased transcription factor binding, and for each of the 22 transcription factors that were examined, at least one mismatch was found that increased the binding affinity. Mismatches also converted non-specific sites into high-affinity sites, and high-affinity sites into 'super sites' that exhibit stronger affinity than any known canonical binding site. Determination of high-resolution X-ray structures, combined with nuclear magnetic resonance measurements and structural analyses, showed that many of the DNA mismatches that increase binding induce distortions that are similar to those induced by protein binding-thus prepaying some of the energetic cost incurred from deforming the DNA. Our work indicates that conformational penalties are a major determinant of protein-DNA recognition, and reveals mechanisms by which mismatches can recruit transcription factors and thus modulate replication and repair activities in the cell10,11.

The Gut of Healthy Infants in the Community as a Reservoir of ESBL and Carbapenemase-Producing Bacteria.

The recent rapid rise of multi-drug resistant Enterobacteriaceae (MDR-E) is threatening the treatment of common infectious diseases. Infections with such strains lead to increased mortality and morbidity. Using a cross-sectional study, we aimed to estimate the prevalence of gut colonization with extended spectrum beta-lactamase (ESBL) producing Enterobacteriaceae among healthy infants born in Pakistan, a setting with high incidence of MDR-E infections. Stool samples were collected from 104 healthy infants between the ages of 5 and 7 months. Enterobacteriaceae isolates were screened for resistance against several antimicrobial classes. Presence of ESBL and carbapenemase genes was determined using multiplex PCR. Sequence types were assigned to individual strains by multi-locus sequence typing. Phylogenetic analysis of Escherichia coli was done using the triplex PCR method. Forty-three percent of the infants were positive for ESBL-producing Enterobacteriaceae, the majority of which were E. coli. We identified several different ESBL E. coli sequence types most of which belonged to the phylogenetic group B2 (23%) or D (73%). The widespread colonization of infants in a developing country with ESBL-producing Enterobacteriaceae is concerning. The multiple sequence types and reported non-human sources support that multiple non-epidemic MDR lineages are circulating in Pakistan with healthy infants as a common reservoir.

Infrared Spectroscopic Observation of a G-C+ Hoogsteen Base Pair in the DNA:TATA-Box Binding Protein Complex Under Solution Conditions.

Hoogsteen DNA base pairs (bps) are an alternative base pairing to canonical Watson-Crick bps and are thought to play important biochemical roles. Hoogsteen bps have been reported in a handful of X-ray structures of protein-DNA complexes. However, there are several examples of Hoogsteen bps in crystal structures that form Watson-Crick bps when examined under solution conditions. Furthermore, Hoogsteen bps can sometimes be difficult to resolve in DNA:protein complexes by X-ray crystallography due to ambiguous electron density and by solution-state NMR spectroscopy due to size limitations. Here, using infrared spectroscopy, we report the first direct solution-state observation of a Hoogsteen (G-C+ ) bp in a DNA:protein complex under solution conditions with specific application to DNA-bound TATA-box binding protein. These results support a previous assignment of a G-C+ Hoogsteen bp in the complex, and indicate that Hoogsteen bps do indeed exist under solution conditions in DNA:protein complexes.

An Atlas of Genetic Variation Linking Pathogen-Induced Cellular Traits to Human Disease.

Pathogens have been a strong driving force for natural selection. Therefore, understanding how human genetic differences impact infection-related cellular traits can mechanistically link genetic variation to disease susceptibility. Here we report the Hi-HOST Phenome Project (H2P2): a catalog of cellular genome-wide association studies (GWAS) comprising 79 infection-related phenotypes in response to 8 pathogens in 528 lymphoblastoid cell lines. Seventeen loci surpass genome-wide significance for infection-associated phenotypes ranging from pathogen replication to cytokine production. We combined H2P2 with clinical association data from patients to identify a SNP near CXCL10 as a risk factor for inflammatory bowel disease. A SNP in the transcriptional repressor ZBTB20 demonstrated pleiotropy, likely through suppression of multiple target genes, and was associated with viral hepatitis. These data are available on a web portal to facilitate interpreting human genome variation through the lens of cell biology and should serve as a rich resource for the research community.

Human genetic and metabolite variation reveals that methylthioadenosine is a prognostic biomarker and an inflammatory regulator in sepsis.

Sepsis is a deleterious inflammatory response to infection with high mortality. Reliable sepsis biomarkers could improve diagnosis, prognosis, and treatment. Integration of human genetics, patient metabolite and cytokine measurements, and testing in a mouse model demonstrate that the methionine salvage pathway is a regulator of sepsis that can accurately predict prognosis in patients. Pathway-based genome-wide association analysis of nontyphoidal Salmonella bacteremia showed a strong enrichment for single-nucleotide polymorphisms near the components of the methionine salvage pathway. Measurement of the pathway's substrate, methylthioadenosine (MTA), in two cohorts of sepsis patients demonstrated increased plasma MTA in nonsurvivors. Plasma MTA was correlated with levels of inflammatory cytokines, indicating that elevated MTA marks a subset of patients with excessive inflammation. A machine-learning model combining MTA and other variables yielded approximately 80% accuracy (area under the curve) in predicting death. Furthermore, mice infected with Salmonella had prolonged survival when MTA was administered before infection, suggesting that manipulating MTA levels could regulate the severity of the inflammatory response. Our results demonstrate how combining genetic data, biomolecule measurements, and animal models can shape our understanding of disease and lead to new biomarkers for patient stratification and potential therapeutic targeting.

A cellular genome-wide association study reveals human variation in microtubule stability and a role in inflammatory cell death.

Pyroptosis is proinflammatory cell death that occurs in response to certain microbes. Activation of the protease caspase-1 by molecular platforms called inflammasomes is required for pyroptosis. We performed a cellular genome-wide association study (GWAS) using Salmonella typhimurium infection of human lymphoblastoid cell lines as a means of dissecting the genetic architecture of susceptibility to pyroptosis and identifying unknown regulatory mechanisms. Cellular GWAS revealed that a common human genetic difference that regulates pyroptosis also alters microtubule stability. An intergenic single-nucleotide polymorphism on chromosome 18 is associated with decreased pyroptosis and increased expression of TUBB6 (tubulin, ß 6 class V). TUBB6 is unique among tubulin isoforms in that its overexpression can completely disrupt the microtubule network. Cells from individuals with higher levels of TUBB6 expression have lower microtubule stability and less pyroptosis. Reducing TUBB6 expression or stabilizing microtubules pharmacologically with paclitaxel (Taxol) increases pyroptosis without affecting the other major readout of caspase-1 activation, interleukin-1ß secretion. The results reveal a new role for microtubules and possibly specific tubulin isoforms in the execution of pyroptosis. Furthermore, the finding that there is common diversity in TUBB6 expression and microtubule stability could have broad consequences for other microtubule-dependent phenotypes, diseases, and pharmacological responses.

Epstein-Barr virus induces global changes in cellular mRNA isoform usage that are important for the maintenance of latency.

Oncogenic viruses promote cell proliferation through the dramatic reorganization of host transcriptomes. In addition to regulating mRNA abundance, changes in mRNA isoform usage can have a profound impact on the protein output of the transcriptome. Using Epstein-Barr virus (EBV) transformation of primary B cells, we have studied the ability of an oncogenic virus to alter the mRNA isoform profile of its host. Using the algorithm called SplicerEX with two complementary Affymetrix microarray platforms, we uncovered 433 mRNA isoform changes regulated by EBV during B-cell transformation. These changes were largely orthogonal with the 2,163 mRNA abundance changes observed during transformation, such that less than one-third of mRNAs changing at the level of isoform also changed in overall abundance. While we observed no preference for a mechanistic class of mRNA isoform change, we detected a significant shortening of 3' untranslated regions and exclusion of cassette exons in EBV-transformed cells relative to uninfected B cells. Gene ontology analysis of the mRNA isoform changes revealed significant enrichment in nucleic acid binding proteins. We validated several of these isoform changes and were intrigued by those in two mRNAs encoding the proteins XBP1 and TCF4, which have both been shown to bind and activate the promoter of the major EBV lytic trans-activator BZLF1. Our studies indicate that EBV latent infection promotes the usage of mRNA isoforms of XBP1 and TCF4 that restrict BZLF1 activation. Therefore, characterization of global changes in mRNA isoform usage during EBV infection identifies a new mechanism for the maintenance of latent infection.

Analysis of Epstein-Barr virus-regulated host gene expression changes through primary B-cell outgrowth reveals delayed kinetics of latent membrane protein 1-mediated NF-κB activation.

Epstein-Barr virus (EBV) is an oncogenic human herpesvirus that dramatically reorganizes host gene expression to immortalize primary B cells. In this study, we analyzed EBV-regulated host gene expression changes following primary B-cell infection, both during initial proliferation and through transformation into lymphoblastoid cell lines (LCLs). While most EBV-regulated mRNAs were changed during the transition from resting, uninfected B cells through initial B-cell proliferation, a substantial number of mRNAs changed uniquely from early proliferation through LCL outgrowth. We identified constitutively and dynamically EBV-regulated biological processes, protein classes, and targets of specific transcription factors. Early after infection, genes associated with proliferation, stress responses, and the p53 pathway were highly enriched. However, the transition from early to long-term outgrowth was characterized by genes involved in the inhibition of apoptosis, the actin cytoskeleton, and NF-κB activity. It was previously thought that the major viral protein responsible for NF-κB activation, latent membrane protein 1 (LMP1), is expressed within 2 days after infection. Our data indicate that while this is true, LCL-level LMP1 expression and NF-κB activity are not evident until 3 weeks after primary B-cell infection. Furthermore, heterologous NF-κB activation during the first week after infection increased the transformation efficiency, while early NF-κB inhibition had no effect on transformation. Rather, inhibition of NF-κB was not toxic to EBV-infected cells until LMP1 levels and NF-κB activity were high. These data collectively highlight the dynamic nature of EBV-regulated host gene expression and support the notion that early EBV-infected proliferating B cells have a fundamentally distinct growth and survival phenotype from that of LCLs.

SplicerEX: a tool for the automated detection and classification of mRNA changes from conventional and splice-sensitive microarray expression data.

The key postulate that one gene encodes one protein has been overhauled with the discovery that one gene can generate multiple RNA transcripts through alternative mRNA processing. In this study, we describe SplicerEX, a novel and uniquely motivated algorithm designed for experimental biologists that (1) detects widespread changes in mRNA isoforms from both conventional and splice sensitive microarray data, (2) automatically categorizes mechanistic changes in mRNA processing, and (3) mitigates known technological artifacts of exon array-based detection of alternative splicing resulting from 5' and 3' signal attenuation, background detection limits, and saturation of probe set signal intensity. In this study, we used SplicerEX to compare conventional and exon-based Affymetrix microarray data in a model of EBV transformation of primary human B cells. We demonstrated superior detection of 3'-located changes in mRNA processing by the Affymetrix U133 GeneChip relative to the Human Exon Array. SplicerEX-identified exon-level changes in the EBV infection model were confirmed by RT-PCR and revealed a novel set of EBV-regulated mRNA isoform changes in caspases 6, 7, and 8. Finally, SplicerEX as compared with MiDAS analysis of publicly available microarray data provided more efficiently categorized mRNA isoform changes with a significantly higher proportion of hits supported by previously annotated alternative processing events. Therefore, SplicerEX provides an important tool for the biologist interested in studying changes in mRNA isoform usage from conventional or splice-sensitive microarray platforms, especially considering the expansive amount of archival microarray data generated over the past decade. SplicerEX is freely available upon request.

The Epstein-Barr virus (EBV)-induced tumor suppressor microRNA MiR-34a is growth promoting in EBV-infected B cells.

Epstein-Barr virus (EBV) infection of primary human B cells drives their indefinite proliferation into lymphoblastoid cell lines (LCLs). B cell immortalization depends on expression of viral latency genes, as well as the regulation of host genes. Given the important role of microRNAs (miRNAs) in regulating fundamental cellular processes, in this study, we assayed changes in host miRNA expression during primary B cell infection by EBV. We observed and validated dynamic changes in several miRNAs from early proliferation through immortalization; oncogenic miRNAs were induced, and tumor suppressor miRNAs were largely repressed. However, one miRNA described as a p53-targeted tumor suppressor, miR-34a, was strongly induced by EBV infection and expressed in many EBV and Kaposi's sarcoma-associated herpesvirus (KSHV)-infected lymphoma cell lines. EBV latent membrane protein 1 (LMP1) was sufficient to induce miR-34a requiring downstream NF-κB activation but independent of functional p53. Furthermore, overexpression of miR-34a was not toxic in several B lymphoma cell lines, and inhibition of miR-34a impaired the growth of EBV-transformed cells. This study identifies a progrowth role for a tumor-suppressive miRNA in oncogenic-virus-mediated transformation, highlighting the importance of studying miRNA function in different cellular contexts.

Teleophthalmology screening for diabetic retinopathy through mobile imaging units within Canada.

BACKGROUND: This study aimed to describe and measure the health results of a Category 3 teleophthalmology screening project for diabetic retinopathy (DR). Implemented through mobile screening imaging units located within pharmacies, the project had the goal of reaching unscreened diabetic patients in urban communities while lowering barriers to screening and saving medical resources. METHODS: Image capture of both eyes of 3505 known diabetic individuals was performed in the provinces of Quebec, British Columbia, Alberta, Manitoba, and Saskatchewan. A photographer performed fundus imaging, and a nurse used mild pupil dilation only when necessary to secure image quality. Screening was provided free of cost in the context of DR health days for DR screening. Through teleophthalmology, ophthalmologists proceeded with data and image interpretation, and timely referral when indicated. RESULTS: This project allowed the resumption of screening of over 38% of the cohort of known diabetics who reported never having undergone any eye examination with pupil dilation, and an additional 30% who reported not having been examined for over 2 years. All known diabetics were under the care of a general physician, and their mean diabetes duration, when known, was 8 years. DR pathology was found in 22.5% (20%-28%) of the cohort, 1.8% requiring urgent referral (within 30 days) as a result of the severity of the DR and 0.6% (0%-1.8%) requiring urgent referral for other reasons. An additional 8.7% (8.1%-19.5%) required ophthalmologic attention within 6 months because of DR and another 2.0% (0%-6.3%) between 6 months and 1 year. Incidental findings were found in 23%, the majority of which were related to cataract and dry macular degeneration. Urgent or significant incidental findings were found in 0.6% of the screened eyes. Pupil dilation with tropicamide 1% was deemed useful or necessary in 33.7% of the cohort. For 0.7% of the cohort, the images could not be interpreted because of poor image quality and for that reason had to be referred for a traditional dilated eye examination. Ophthalmologists were relieved of the examination of 85.6% of the screened diabetic individuals who benefited from screening without requiring a traditional ophthalmologic examination. On the other hand, ophthalmologists were required to provide urgent (within 30 days) services to 2% of the cohort, either because of threatening DR or because of incidental findings requiring rapid ophthalmologic attention. INTERPRETATION: This screening strategy for DR through mobile teleophthalmology imaging units efficiently lowered barriers to screening and created new screening opportunities for a large number of known diabetic individuals who were lost to the traditional health system. It has the potential to provide better outreach to diabetic populations while identifying individuals truly in need of the services of an ophthalmologist; at the same time it maximizes the use of limited ophthalmologic resources while favouring multidisciplinary collaborations. The significant incidental findings associated with screening highlight the need for ophthalmologic competencies during DR screening within a teleophthalmology approach. Further involvement of government health authorities is pivotal in embracing the opportunities provided by emerging technologies such as teleophthalmology and translating them into better outreach services to diabetic populations and thus better visual health results.